Ultrafast nonequilibrium dynamics of rotons in superfluid helium

Short-time dynamics of superfluids far from equilibrium remains largely unknown, despite its importance for key processes in these systems. Here, we describe a method for locally perturbing the density of superfluid helium via the excitation of roton pairs with ultrashort laser pulses. By measuring...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 120; no. 17; p. e2303231120
Main Authors Milner, Alexander A., Stamp, Philip C. E., Milner, Valery
Format Journal Article
LanguageEnglish
Published United States National Academy of Sciences 25.04.2023
Subjects
Bose-Einstein condensates
Elementary excitations
Fluids
Helium
Liquid helium
Nucleation
Perturbation
Physical Sciences
Rotons
Superfluidity
Time dependence
Time measurement
liquid helium
superfluid
roton
many-body
ultrafast
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Summary:Short-time dynamics of superfluids far from equilibrium remains largely unknown, despite its importance for key processes in these systems. Here, we describe a method for locally perturbing the density of superfluid helium via the excitation of roton pairs with ultrashort laser pulses. By measuring the time dependence of this perturbation, we track the nonequilibrium dynamics of the two-roton states on femtosecond and picosecond timescales. Our results reveal an ultrafast equilibration of roton pairs as they thermalize with the colder equilibrium quasiparticle gas. Future applications of this technique to different temperature and pressure regimes, in various superfluids, will enable to probe rapid nucleation and decay processes, as well as metastable Bose–Einstein condensates of rotons and roton pairs.
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Edited by J. C. Davis, University of Oxford, United Kingdom; received February 24, 2023; accepted March 15, 2023
ISSN:0027-8424
1091-6490
1091-6490
DOI:10.1073/pnas.2303231120